1. Field of the Invention
The present invention relates to stop line recognition devices that recognize a stop line in front of the carriageway of a vehicle.
2. Description of the Related Art
In recent years, various driving support systems for vehicles have been under development as part of efforts of the Intelligent Transport System (ITS). For example, Japanese Unexamined Patent Application Publication No. 2005-170154 (hereunder referred to as “Patent Document 1”) discloses a technology that performs image recognition such as template matching to an image signal captured by a charge-coupled device (CCD) camera to extract a specific object that indicates that an own vehicle should stop, and performs driving support for having the vehicle stop based on the extracted specific object. According to the technology of Patent Document 1, a stop lamp of a preceding vehicle that is emitting light to indicate that the preceding vehicle is performing a braking operation, a traffic signal displaying red light and a stop sign and the like are detected as the specific object and the position of a stop line, and further the like is recognized.
Since the stop line provided on the road is generally used only as marker for stopping at an intersection and the like, and, unlike a preceding vehicle and a traffic signal, is not an object for directly determining whether it is necessary for the vehicle to stop or not, there is little need to constantly recognize the stop line upon performing driving support such as stop control of the own vehicle.
Therefore, if the recognition of the stop line is constantly performed at a level similar to a level for the preceding vehicle, traffic signal and the like, unnecessary calculation load may be increased, which may result in a very longer processing time of driving support control itself and the like.
Furthermore, for example, when a plurality of roadside trees' shadows cross over the carriageway of the own vehicle, a light and dark pattern created on the road by the shadows may be erroneously recognized as the stop line on an image: the constant recognition of the stop line may also decrease the recognition accuracy of the stop line.